Method and apparatus for assessing left ventricular function and optimizing cardiac pacing intervals based on left ventricular wall motion

ABSTRACT

A system and method for monitoring left ventricular (LV) lateral wall motion and for optimizing cardiac pacing intervals based on left ventricular lateral wall motion is provided. The system includes an implantable or external cardiac stimulation device in association with a set of leads including a left ventricular epicardial or coronary sinus lead equipped with a motion sensor electromechanically coupled to the lateral wall of the left ventricle. The device receives and processes wall motion sensor signals to determine a signal characteristic indicative of systolic LV lateral wall motion or acceleration. An automatic pacing interval optimization method evaluates the LV lateral wall motion during varying pacing interval settings, including atrial-ventricular intervals and inter-ventricular intervals and selects the pacing interval setting(s) that correspond to LV lateral wall motion associated with improved cardiac synchrony and hemodynamic performance.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesfor monitoring or treating a cardiac abnormalities and more particularlyto a device and method for delivering cardiac pacing impulses atinter-chamber intervals that are optimized based on left ventricularwall motion monitoring.

BACKGROUND OF THE INVENTION

Evaluation of left ventricular function is of interest for bothdiagnostic and therapeutic applications. During normal cardiac function,the left atrium, the left ventricle, and the right ventricle observeconsistent time-dependent relationships during the systolic(contractile) phase and the diastolic (relaxation) phase of the cardiaccycle. During cardiac dysfunction associated with pathologicalconditions or following cardiac-related surgical procedures, thesetime-dependent mechanical relationships are often altered. Thisalteration, when combined with the effects of weakened cardiac muscles,reduces the ability of the ventricle to generate contractile strengthresulting in hemodynamic insufficiency.

Ventricular dyssynchrony following coronary artery bypass graft (CABG)surgery is a problem encountered relatively often, requiringpost-operative temporary pacing. Atrio-biventricular pacing has beenfound to improve post-operative hemodynamics following such procedures.

Ventricular resynchronization therapy has been clinically demonstratedto improve indices of cardiac function in patients suffering fromcongestive heart failure. Cardiac pacing may be applied to one or bothventricles or multiple heart chambers, including one or both atria, toimprove cardiac chamber coordination, which in turn is thought toimprove cardiac output and pumping efficiency. Clinical follow-up ofpatients undergoing resynchronization therapy has shown improvements inhemodynamic measures of cardiac function, left ventricular volumes, andwall motion. However, not all patients respond favorably to cardiacresynchronization therapy. Physicians are challenged in selectingpatients that will benefit and in selecting the optimal pacing intervalsapplied to resynchronize the heart chamber contractions.

Selection of atrial-ventricular (A-V) and inter-ventricular (V-V) pacingintervals may be based on echocardiographic studies performed todetermine the settings resulting in the best hemodynamic response.However, this approach provides only an open-loop method. Afterevaluating the hemodynamic effect of varying combinations of pacingintervals, a physician must manually select and program the desiredparameters and assume that the patient's device optimal settings remainunchanged until a subsequent re-optimization visit. Automated methodsfor selecting pacing intervals during multi-chamber pacing have beenproposed. A four-chamber pacing system that includes impedance sensingfor determining the timing of right heart valve closure or rightventricular contraction and adjusting the timing of delivery of leftventricular pace pulses is generally disclosed in U.S. Pat. No.6,223,082 issued to Bakels, et al., incorporated herein by reference inits entirety. Programmable coupling intervals selected so as to provideoptimal hemodynamic benefit to the patient in an implantablemultichamber cardiac stimulation device are generally disclosed in U.S.Pat. No. 6,473,645 issued to Levine, incorporated herein by reference inits entirety.

Doppler tissue imaging has been used clinically to evaluate myocardialshortening rates and strength of contraction. This rate of contractionhas been investigated as a determinant of clinical health of theventricle. Doppler tissue imaging has also been used to investigatecoordination between septal and lateral wall motion for predicting whichpatients are likely to benefit from cardiac resynchronization therapy.Evidence suggests patient response is dependent on the degree ofventricular synchrony before and after therapy. Doppler tissue imagingstudies have shown that the left ventricular mid to mid-basal segmentsshow the greatest improvement in shortening following cardiacresynchronization therapy. Detection and monitoring of left ventricularwall motion, therefore, would be useful in optimizing cardiacresynchronization therapy.

Implantable sensors for monitoring heart wall motion have beendescribed. A sensor implanted in the heart mass for monitoring heartfunction by monitoring the momentum or velocity of the heart mass isgenerally disclosed in U.S. Pat. No. 5,454,838 issued to Vallana et al.A catheter for insertion into the ventricle for monitoring cardiaccontractility having an acceleration transducer at or proximate thecatheter tip is generally disclosed in U.S. Pat. No. 6,077,236 issued toCunningham. Implantable leads incorporating accelerometer-based cardiacwall transducers are generally disclosed in U.S. Pat. No. 5,628,777issued to Moberg, et al. A device for sensing natural heart accelerationis generally disclosed in U.S. Pat. No. 5,693,075, issued to Plicchi, etal. A system for myocardial tensiometery including a tensiometricelement disposed at a location subject to bending due to cardiaccontractions is generally disclosed in U.S. Pat. No. 5,261,418 issued toFerek-Petric et al. All of the above-cited patents are herebyincorporated herein by reference in their entirety.

Detection of peak endocardial wall motion in the apex of the rightventricle for optimizing A-V intervals has been validated clinically. Asystem and method for using cardiac wall motion sensor signals toprovide hemodynamically optimal values for heart rate and AV intervalare generally disclosed in U.S. Pat. No. 5,549,650 issued to Bornzin, etal., incorporated herein by reference in its entirety. A cardiacstimulating system designed to automatically optimize both the pacingmode and one or more pacing cycle parameters in a way that results inoptimization of a cardiac performance parameter, including for exampleheart accelerations, is generally disclosed in U.S. Pat. No. 5,540,727,issued to Tockman, et al.

A need remains, however, for providing a device and method formonitoring left ventricular wall motion and for selecting optimalcardiac pacing intervals that produce the greatest improvement in leftventricular wall motion during multi-chamber or biventricular pacingdelivered to improve heart chamber synchronization, chronically oracutely. Improved left ventricular wall motion is expected to reflect animprovement in cardiac chamber synchrony and generally result in a netimprovement in cardiac efficiency.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for assessing leftventricular function and optimizing cardiac pacing intervals based ondetection of left ventricular wall motion. In one embodiment, thepresent invention is realized in a cardiac resynchronization system thatincludes an implantable multi-chamber pulse generator and associatedlead system wherein a left ventricular coronary sinus lead or leftventricular epicardial lead is provided with a sensor for detecting leftventricular wall motion. In an alternative embodiment, a temporary,external pulse generator is coupled to temporary pacing leads includinga left ventricular temporary pacing lead equipped with a wall motionsensor. For each embodiment of the present invention, in addition to thepulse generator appropriate defibrillator circuitry may be employed inelectrical communication to suitable

In a preferred embodiment, the wall motion sensor is an accelerometer,which may be a uniaxial, biaxial, or triaxial accelerometer.Alternatively, the wall motion sensor may be provided as other types ofpiezoelectric sensors, optical sensors, Hall-effect type sensors,capacitive, resistive, inductive or any other type of sensor capable ofgenerating a signal proportional to left-ventricular free wall motion oracceleration. A left ventricular wall motion sensor is preferably placedin or proximate the mid- or mid-basal left ventricular free wallsegments.

The implantable or external pulse generator receives and processes thewall motion sensor signal during an automated testing routine, whichincludes application of varying resynchronization pacing intervals,including atrial-ventricular and/or ventricular-ventricular intervals.Signal processing is performed to time-average the wall motion signaland derive averaged signal parameters as indices of left ventricularfree wall motion or acceleration. The pacing intervals producing thegreatest improvement in left ventricular wall motion, based on the wallmotion sensor data, can be automatically selected for delivering cardiacresynchronization therapy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardialleads.

FIG. 1B depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardial leadsand an additional left ventricular epicardial lead equipped with a wallmotion sensor.

FIG. 2 is a schematic block diagram of the multi-chamber pacemaker ofFIG. 1A capable of delivering a resynchronization therapy and processingleft ventricular wall motion sensor signal input.

FIG. 3 depicts an alternative, epicardial lead system coupled to apatient's heart.

FIG. 4 is a flow chart providing an overview of a method for optimizingcardiac pacing intervals based on monitoring LV wall motion.

FIG. 5 is a flow chart summarizing steps included in a method fordetermining an optimal AV interval based on left ventricular wall motionfor use in the method of FIG. 4.

FIG. 6 is a graph of sample, experimental LV wall motion data collectedfrom an accelerometer during atrio-biventricular pacing at varying A-Vintervals and simultaneous right and left ventricular pacing (V-Vinterval set to 0 ms).

FIG. 7 is a flow chart summarizing steps included in a method fordetermining an optimal V-V interval based on left ventricular wallmotion for use the method FIG. 4.

FIG. 8 is a graph of sample, experimental LV wall motion data collectedfrom an accelerometer during atrio-biventricular pacing at varying V-Vintervals and an A-V interval previously optimized to 130 ms.

FIG. 9 is a flow chart summarizing steps included in a method formonitoring left ventricular function based on lateral wall motion.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, the present invention is directed toward providing amethod and apparatus for evaluating left ventricular function andselecting cardiac pacing intervals for the purposes of restoring normalventricular synchrony based on monitoring left ventricular free wallmotion. The present invention is useful in optimizing atrial-ventricularand inter-ventricular pacing intervals during chronic resynchronizationtherapy used for treating heart failure. The present invention is alsouseful in selecting pacing parameters used during temporary pacingapplied for treating post-operative ventricular dyssynchrony. As such,the present invention may be embodied in an implantable cardiac pacingsystem including a dual chamber or multichamber pacemaker and associatedset of leads. Alternatively, the present invention may be embodied in atemporary pacing system including an external pacing device withassociated temporary pacing leads.

FIG. 1A depicts an exemplary implantable, multi-chamber cardiacpacemaker 14 in which the present invention may be implemented. Themulti-chamber pacemaker 14 is provided for restoring ventricularsynchrony by delivering pacing pulses to one or more heart chambers asneeded to control the heart activation sequence. The pacemaker 14 isshown in communication with a patient's heart 10 by way of three leads16, 32 and 52. The heart 10 is shown in a partially cut-away viewillustrating the upper heart chambers, the right atrium (RA) and leftatrium (LA), and the lower heart chambers, the right ventricle (RV) andleft ventricle (LV), and the coronary sinus (CS) extending from theopening in the right atrium laterally around the atria to form the greatcardiac vein 48, which branches to form inferior cardiac veins.

The pacemaker 14, also referred to herein as the “implantable pulsegenerator” or “IPG,” is implanted subcutaneously in a patient's bodybetween the skin and the ribs. Three transvenousendocardial leads 16, 32and 52 connect the IPG 14 with the RA, the RV and the LV, respectively.Each lead has at least one electrical conductor and pace/senseelectrode. A remote indifferent can electrode 20 is formed as part ofthe outer surface of the housing of the IPG 14. The pace/senseelectrodes and the remote indifferent can electrode 20 can beselectively employed to provide a number of unipolar and bipolarpace/sense electrode combinations for pacing and sensing functions.

The depicted bipolar endocardial RA lead 16 is passed through a veininto the RA chamber of the heart 10, and the distal end of the RA lead16 is attached to the RA wall by an attachment mechanism 17. The bipolarendocardial RA lead 16 is formed with an in-line connector 13 fittinginto a bipolar bore of IPG connector block 12 that is coupled to a pairof electrically insulated conductors within lead body 15 and connectedwith distal tip RA pace/sense electrode 19 and proximal ring RApace/sense electrode 21 provided for achieving RA pacing and sensing ofRA electrogram (EGM) signals.

Bipolar, endocardial RV lead 32 is passed through the RA into the RVwhere its distal ring and tip RV pace/sense electrodes 38 and 40 arefixed in place in the apex by a conventional distal attachment mechanism41. The RV lead 32 is formed with an in-line connector 34 fitting into abipolar bore of IPG connector block 12 that is coupled to a pair ofelectrically insulated conductors within lead body 36 and connected withdistal tip RV pace/sense electrode 40 and proximal ring RV pace/senseelectrode 38 provided for RV pacing and sensing of RV EGM signals. RVlead 32 may optionally include a RV wall motion sensor 60. RV wallmotion sensor 60 may be positioned into or proximate the RV apex fordetecting motion or acceleration of the RV apical region. Implantationof an acceleration sensor in the right ventricle is generally disclosedin the above-cited U.S. Pat. No. 5,693,075 issued to Plicchi, et al.

In this illustrated embodiment, a unipolar, endocardial LV CS lead 52 ispassed through the RA, into the CS and further into a cardiac vein toextend the distal LV CS pace/sense electrode 50 alongside the LV chamberto achieve LV pacing and sensing of LV EGM signals. The LV CS lead 52 iscoupled at the proximal end connector 54 fitting into a bore of IPGconnector block 12. A small diameter unipolar lead body 56 is selectedin order to lodge the distal LV CS pace/sense electrode 50 deeply in acardiac vein branching from the great cardiac vein 48.

In accordance with the present invention, the coronary sinus lead 52 isprovided with a sensor 62 capable of generating a signal proportional tothe motion of the left ventricular free wall. Sensor 62 is preferablyembodied as a uniaxial, biaxial, or triaxial accelerometer contained ina capsule of a relatively small size and diameter such that it may beincluded in a coronary sinus lead without substantially increasing thelead diameter or impairing the ability to steer the lead to a leftventricular pacing and sensing site. Radial information may not be asvaluable in assessing LV wall motion and optimizing pacing intervals aslongitudinal information, therefore, a uniaxial accelerometer may beadequate for these purposes. Sensor 62 may alternatively be provided asanother type of sensor such as an optical, acoustical, or Hall effectsensor or a sensor having piezoelectric, inductive, capacitive,resistive, or other elements which produce a variable signalproportional to left ventricular wall motion or acceleration. Sensor 62is preferably located on CS lead 52 such that when CS lead 52 ispositioned for LV pacing and sensing, sensor 62 is located approximatelyover the left ventricular free wall mid-lateral to mid-basal segments.The depicted positions of the leads and electrodes shown in FIG. 1A inor about the right and left heart chambers are approximate and merelyexemplary. For example, a left ventricular wall motion sensor 62 mayalternatively be located on CS lead 52 such that sensor 62 is positionedin the coronary sinus, in the great cardiac vein, or in any accessibleinferior cardiac vein. Furthermore, it is recognized that alternativeleads and pace/sense electrodes that are adapted for placement at pacingor sensing sites on or in or relative to the RA, LA, RV and LV may beused in conjunction with the present invention.

In a four chamber embodiment, LV CS lead 52 could bear a proximal LA CSpace/sense electrode positioned along the lead body to lie in the largerdiameter coronary sinus adjacent the LA for use in pacing the LA orsensing LA EGM signals. In that case, the lead body 56 would encase aninsulated lead conductor extending proximally from the more proximal LACS pace/sense electrode(s) and terminating in a bipolar connector 54.

FIG. 1B depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardial leadsand an additional left ventricular epicardial lead equipped with wallmotion sensor 62. Patients may already be implanted with a transvenouslead system that includes a coronary sinus lead 52 that is not equippedwith a wall motion sensor. Such patients may benefit from the placementof an epicardial lead 64 equipped with wall motion sensor 62 coupled toIPG 14 via a connector 66 so as to provide an LV wall motion signal foruse in a closed-loop feedback system for providing resynchronizationtherapy at optimal pacing intervals.

Epicardial lead 64 is provided with a fixation member 63 which may serveadditionally as a pacing and/or sensing electrode. In some cases, anepicardial lead may be preferred over a coronary sinus lead due to thedifficulty in advancing a coronary sinus lead into a cardiac vein overthe LV free wall. Placement of a coronary sinus lead can be a cumbersometask due to the tortuosity of the cardiac veins. Therefore, it may bedesirable, at least in some patients, to provide an epicardial lead thatcan be positioned on the LV lateral wall for pacing, EGM sensing andwall motion monitoring, eliminating the need for a coronary sinus lead.Alternatively, it may be desirable to deploy a small diameter coronarysinus lead for LV pacing and EGM sensing with a separate LV epicardiallead positioned for sensing LV lateral wall motion.

The embodiment generally shown in FIG. 1B is particularly advantageousfor use in selecting resynchronization therapy pacing sites. Withepicardial lead 64 fixed at a desired location for assessing LV wallmotion, the effect of pacing at different locations in one or more heartchambers can be evaluated by deploying the transvenous pacing leads 16,32 and 52 to different locations. In particular, coronary sinus lead 52may be advanced to different locations until an optimal location isidentified based on analysis of the signal from LV wall motion sensor62. By providing wall motion sensor 62 on a separate, epicardial lead64, the position of pacing electrode 50, provided on coronary sinus lead52, may be adjusted independently of sensor 62. If the position ofpacing electrode 50 needs adjusting, wall motion sensor 62 may remainfixed at a desired LV lateral wall location thereby allowing comparisonsto be made between measurements repeated at the same location fordifferent pacing intervals and/or pacing sites.

FIG. 2 is a schematic block diagram of an exemplary multi-chamber IPG14, such as that shown in FIG. 1A or 1B, that provides delivery of aresynchronization therapy and is capable of processing left ventricularwall motion sensor signal input. The IPG 14 is preferably amicroprocessor-based device. Accordingly, microprocessor-based controland timing system 102, which varies in sophistication and complexitydepending upon the type and functional features incorporated therein,controls the functions of IPG 14 by executing firmware and programmedsoftware algorithms stored in associated RAM and ROM. Control and timingsystem 102 may also include a watchdog circuit, a DMA controller, ablock mover/reader, a CRC calculator, and other specific logic circuitrycoupled together by on-chip data bus, address bus, power, clock, andcontrol signal lines in paths or trees in a manner known in the art. Itwill also be understood that control and timing functions of IPG 14 canbe accomplished with dedicated circuit hardware or state machine logicrather than a programmed microcomputer.

The IPG 14 includes interface circuitry 104 for receiving signals fromsensors and pace/sense electrodes located at specific sites of thepatient's heart chambers and delivering cardiac pacing to control thepatient's heart rhythm and resynchronize heart chamber activation. Theinterface circuitry 104 therefore includes a therapy delivery system 106intended for delivering cardiac pacing impulses under the control ofcontrol and timing system 102. Delivery of pacing pulses to two or moreheart chambers is controlled in part by the selection of programmablepacing intervals, which can include atrial-atrial (A-A),atrial-ventricular (A-V), and ventricular-ventricular (V-V) intervals.

Physiologic input signal processing circuit 108 is provided forreceiving cardiac electrogram (EGM) signals for determining a patient'sheart rhythm. Physiologic input signal processing circuit 108additionally receives signals from left ventricular wall motion sensor62, and optionally RV wall motion sensor 60, and processes these signalsand provides signal data to control and timing system 102 for furthersignal analysis. For purposes of illustration of the possible uses ofthe invention, a set of lead connections are depicted for makingelectrical connections between the therapy delivery system 106 and theinput signal processing circuit 108 and sets of pace/sense electrodes,wall motion sensors, and any other physiological sensors located inoperative relation to the RA, LA, RV and LV.

Control and timing system 102 controls the delivery of bi-atrial,bi-ventricular, or multi-chamber cardiac pacing pulses at selectedintervals intended to improve heart chamber synchrony. The delivery ofpacing pulses by IPG 14 may be provided according to programmable pacingintervals, such as programmable conduction delay window times asgenerally disclosed in U.S. Pat. No. 6,070,101 issued to Struble et al.,incorporated herein by reference in its entirety, or programmablecoupling intervals as generally disclosed in above-cited U.S. Pat. No.6,473,645 issued to Levine. Selection of the programmable pacingintervals is preferably based on a determination of left ventricularwall motion derived from sensor 62 signals as will be described ingreater detail below.

The therapy delivery system 106 can optionally be configured to includecircuitry for delivering cardioversion/defibrillation therapy inaddition to cardiac pacing pulses for controlling a patient's heartrhythm. Accordingly, leads in communication with the patient's heartcould additionally include high-voltage cardioversion or defibrillationshock electrodes.

A battery 136 provides a source of electrical energy to power componentsand circuitry of IPG 14 and provide electrical stimulation energy fordelivering electrical impulses to the heart. The typical energy sourceis a high energy density, low voltage battery 136 coupled with a powersupply/POR circuit 126 having power-on-reset (POR) capability. The powersupply/POR circuit 126 provides one or more low voltage power (Vlo), thePOR signal, one or more reference voltage (VREF) sources, currentsources, an elective replacement indicator (ERI) signal, and, in thecase of a cardioversion/defibrillator capabilities, high voltage power(Vhi) to the therapy delivery system 106. Not all of the conventionalinterconnections of these voltages and signals are shown in FIG. 2.

Current electronic multi-chamber pacemaker circuitry typically employsclocked CMOS digital logic ICs that require a clock signal CLK providedby a piezoelectric crystal 132 and system clock 122 coupled thereto aswell as discrete components, e.g., inductors, capacitors, transformers,high voltage protection diodes, and the like that are mounted with theICs to one or more substrate or printed circuit board. In FIG. 2, eachCLK signal generated by system clock 122 is routed to all applicableclocked logic via a clock tree. The system clock 122 provides one ormore fixed frequency CLK signal that is independent of the batteryvoltage over an operating battery voltage range for system timing andcontrol functions and in formatting uplink telemetry signaltransmissions in the telemetry I/O circuit 124.

The RAM registers included in microprocessor-based control and timingsystem 102 may be used for storing data compiled from sensed EGMsignals, wall motion signals, and/or relating to device operatinghistory or other sensed physiologic parameters for uplink telemetrytransmission upon receipt of a retrieval or interrogation instructionvia a downlink telemetry transmission. Criteria for triggering datastorage can be programmed via down linked instructions and parametervalues. Physiologic data, including wall motion data, may be stored on atriggered or periodic basis or by detection logic within the physiologicinput signal processing circuit 108. In some cases, the IPG 14 includesa magnetic field sensitive switch 130 that closes in response to amagnetic field, and the closure causes a magnetic switch circuit 120 toissue a switch closed (SC) signal to control and timing system 102 whichresponds in a magnet mode. For example, the patient may be provided witha magnet 116 that can be applied over the subcutaneously implanted IPG14 to close switch 130 and prompt the control and timing system todeliver a therapy and/or store physiologic data. Event related data,e.g., the date and time and current pacing parameters, may be storedalong with the stored physiologic data for uplink telemetry in a laterinterrogation session.

Uplink and downlink telemetry capabilities are provided to enablecommunication with either a remotely located external medical device ora more proximal medical device on or in the patient's body. Stored EGM,or LV wall motion data as well as real-time generated physiologic dataand non-physiologic data can be transmitted by uplink RF telemetry fromthe IPG 14 to the external programmer or other remote medical device 26in response to a downlink telemetered interrogation command. As such, anantenna 128 is connected to radio frequency (RF) transceiver circuit 124for the purposes of uplink/downlink telemetry operations. Telemeteringboth analog and digital data between antenna 128 and an external device26, also equipped with an antenna 118, may be accomplished usingnumerous types of telemetry systems known in the art for use inimplantable devices.

The physiologic input signal processing circuit 108 includes at leastone electrical signal amplifier circuit for amplifying, processing andin some cases detecting sense events from characteristics of theelectrical sense signal or sensor output signal. The physiologic inputsignal processing circuit 108 may thus include a plurality of cardiacsignal sense channels for sensing and processing cardiac signals fromsense electrodes located in relation to a heart chamber. Each suchchannel typically includes a sense amplifier circuit for detectingspecific cardiac events and an EGM amplifier circuit for providing anEGM signal to the control and timing system 102 for sampling, digitizingand storing or transmitting in an uplink transmission. Atrial andventricular sense amplifiers include signal processing stages fordetecting the occurrence of a P-wave or R-wave, respectively andproviding an atrial sense or ventricular sense event signal to thecontrol and timing system 102. Timing and control system 102 responds inaccordance with its particular operating system to deliver or modify apacing therapy, if appropriate, or to accumulate data for uplinktelemetry transmission in a variety of ways known in the art. Thus theneed for pacing pulse delivery is determined based on EGM signal inputaccording to the particular operating mode in effect. The intervals atwhich pacing pulses are delivered are preferably determined based on anassessment of LV wall motion data.

As such, input signal processing circuit 108 further includes signalprocessing circuitry for receiving, amplifying, filtering, averaging,digitizing or otherwise processing the LV wall motion sensor signal. Ifadditional wall motion sensors are included in the associated leadsystem, for example a RV wall motion sensor, additional wall motionsignal processing circuitry may be provided as needed. Wall motionsignal processing circuitry is further provided for detection and/ordetermination of one or more wall motion signal characteristics such asmaximum and minimum peak amplitudes, slopes, integrals, or other time orfrequency domain signal characteristics that may be used as indices ofwall motion or correlates to hemodynamic performance. Such wall motionsignal characteristic values determined from an LV wall motion sensorsignal are made available to control and timing system 102 via LV MOTIONsignal line for use in algorithms performed for identifying pacingintervals producing optimal LV wall motion. If an RV wall motion sensoris present, an additional RV MOTION signal line provides RV wall motionsignal data to control and timing system 102.

FIG. 3 depicts an alternative, epicardial lead system coupled to apatient's heart. Epicardial leads may be used in conjunction with eitherchronically implantable or temporary external pacing systems. In theembodiment shown, RV epicardial lead 80 is shown fixed via an activefixation electrode 82 near the apex of the RV such that the activefixation electrode 82 is positioned in contact with the RV epicardialtissue for pacing and sensing in the right ventricle. RV epicardial lead80 may optionally be equipped with an RV wall motion sensor 84 fordetecting motion or acceleration of the RV apical region. LV epicardiallead 70 is shown fixed via an active fixation electrode 72 in the LVfree wall such that active fixation electrode 72 is positioned incontact with the LV epicardial tissue for pacing and sensing in the leftventricle. LV epicardial lead 70 is equipped with a wall motion sensor74 for detecting motion or acceleration of the LV free wall. Epicardiallead systems may further include epicardial RA and/or LA leads. Variouscombinations of epicardial and transvenous endocardial leads are alsopossible for use with biventricular or multichamber cardiac stimulationsystems.

In FIG. 3, RV and LV epicardial leads 70 and 80 are shown coupled to anexternal, temporary cardiac pacing device 90. External pacing device 90is preferably a microprocessor controlled device includingmicroprocessor 96 with associated RAM and ROM for storing and executingfirmware and programmable software for controlling the delivery ofpacing pulses to LV and RV pace/sense electrodes 72 and 82. Externaldevice 90 receives signals from and delivers electrical pulses to LV andRV pace/sense electrodes 72 and 82 via conductors included in LVepicardial lead body 76 and RV epicardial lead body 86. EGM signals, LVwall motion signals, and optionally RV wall motion signals are receivedas input to input signal processing circuitry 94. Pacing impulses aredelivered by output circuitry 92 as needed, based on sensed EGM signals,at intervals determined based on signals received from LV wall motionsensor 74 as will be described in greater detail below. It is recognizedthat an epicardial lead system such as that shown in FIG. 3 thatincludes an LV wall motion sensor and optionally an RV wall motionsensor may alternatively be used in conjunction with an implantablepacing system, such as the multi-chamber system described above andshown in FIGS. 1 and 2.

External device 90 of FIG. 3 and implantable device 14 of FIGS. 1 and 2are shown to provide both sensing/monitoring and pacing deliverycapabilities. Certain device features may be enabled or disabled asdesired. For example, monitoring of LV wall motion without delivery of apacing therapy may be desired. LV wall motion sensor signal data maytherefore be received, processed and stored by an implantable orexternal device for later analysis and review by a clinician.

FIG. 4 is a flow chart providing an overview of a method for optimizingcardiac pacing intervals based on monitoring LV wall motion. Method 200begins at step 205 by monitoring LV wall motion. Preferably a wallmotion sensor is implanted in or proximate to the LV free wall asdescribed above. More preferably, an LV wall motion signal is obtainedfrom an accelerometer located on a coronary sinus lead advanced suchthat the accelerometer is positioned in a cardiac vein over themid-lateral, mid-basal or basal segment of the left ventricular freewall.

At step 210, an optimal A-V interval is determined if the pacing mode isan atrioventricular or atrio-biventricular mode. Depending on the dualchamber or multichamber pacing system being used, a right A-V intervalor a left A-V interval or both may be determined. For the embodimentshown in FIG. 1A, an optimal right atrial to right ventricle interval isdetermined. However, in other embodiments, the left atrial-leftventricular interval is optimized based on LV wall motion to ensureoptimal filling of the LV. A method for determining an optimal A-Vinterval based on LV wall motion will be described in conjunction withFIG. 5. At step 215, the A-V interval is automatically adjusted to theoptimal A-V interval determined at step 210.

At step 220, the optimal V-V interval is determined for bi-ventricularor atrio-biventricular pacing modes. A method for optimizing the V-Vinterval based on LV wall motion will be described in conjunction withFIG. 7. At step 225, the V-V interval is automatically adjusted to theoptimal V-V interval determined at step 220. After adjusting the V-Vinterval, an optional step 230 may be performed to re-optimize the A-Vinterval. Verification of the provisionally determined optimal A-Vinterval is made by re-determining the optimal A-V interval duringbiventricular pacing at the newly optimized V-V interval. The A-Vinterval may be re-adjusted accordingly if a different A-V interval isidentified as being optimal during pacing at the optimal V-V interval.

FIG. 5 is a flow chart summarizing steps included in a method fordetermining an optimal AV interval based on left ventricular wall motionfor use in method 200 of FIG. 4. Method 300 begins at step 305 bysetting the V-V interval to a nominal setting, preferably to 0 ms suchthat the left and right ventricles are paced simultaneously. At step 310an A-V test interval is set. A number of predetermined test A-Vintervals may be programmed. In a patient with intact atrioventricularconduction, the A-V intervals tested may include the intrinsic A-Vinterval. In order to allow intrinsic A-V conduction, the A-V intervalis set at a maximum setting or a setting longer than the intrinsic A-Vconduction time. The intrinsic A-V conduction time may be determined bymeasuring the interval from an atrial pacing pulse to a subsequentlysensed R-wave. Remaining test A-V intervals may be applied at decreasingincrements from the intrinsic A-V interval. Alternatively, test A-Vintervals may be applied randomly ranging from 0 ms to the intrinsic A-Vinterval. If atrioventricular conduction is not intact, a set of testA-V intervals may be selected over a predefined range, for example arange from 0 ms to on the order of 250 ms.

At step 315 a data collection window is set. LV wall motion data ispreferably collected during systolic contraction such that accelerationor motion of the left ventricular wall segment over which the wallmotion sensor is positioned may be measured. However, LV wall motiondata may be acquired for use in assessing LV function or optimizing atherapy during the isovolumic contraction phase, the ejection phase,isovolumic relaxation, early diastolic filling, and/or late diastolicfilling. The data collection window may be a fixed time intervalfollowing a delivered ventricular or atrial pacing pulse (or sensedR-wave if intrinsic A-V conduction is being tested in patients withoutAV block). A data collection window may be set as a time intervalbeginning at the delivery of a ventricular pacing pulse with a durationon the order of 30 to 180 ms, for example.

At step 320, the LV wall motion signal is sampled during the datacollection window for each cardiac cycle during a predetermined timeinterval or for a predetermined number of cardiac cycles. In analternative embodiment, the LV wall motion signal may be acquiredcontinuously during the predetermined time interval or number of cardiaccycles and subsequently processed to separate components associated withthe maximum acceleration phase of the systolic contraction. The timeinterval or number of cardiac cycles preferably extends over at leastone respiration cycle such that averaging of the LV wall motion signalover a respiration cycle may be performed to eliminate variations in theLV wall motion measurements due to respiration. In one embodiment, thestart and stop of wall motion data acquisition may be triggered bysensing a respiration cycle. Respiration may be detected based onimpedance measurements or other methods known in the art.

At decision step 325, verification of a stable heart rate during thedata acquisition interval is performed. Heart rate instability, such asthe presence of ectopic heart beats or other irregularities, wouldproduce anomalous LV wall motion data. As such, the heart ratepreferably stays within a specified range. In one embodiment, heart ratestability may be verified by determining the average and standarddeviation of the cardiac cycle length during the data acquisitionperiod. The cardiac cycle length may be determined as the intervalbetween consecutive ventricular events including ventricular pacingpulses and any sensed R-waves. If the average cardiac cycle length orits standard deviation falls outside a predefined range, the data isconsidered unreliable. Data acquisition may be repeated by returning tostep 315 until reliable data is collected for the current test intervalsetting.

At step 330, signal averaging is performed to minimize the effects ofrespiration-related or other noise. The signals acquired during eachcardiac cycle over the data collection interval are averaged to obtainan overall average LV wall motion signal. At step 340, one or moresignal features are determined from the averaged signal as a measurementof LV wall motion and stored in device memory with corresponding testinterval information. Preferably, the maximum amplitude of anaccelerometer signal or its maximum excursion determined as thedifference between the maximum and minimum peak amplitude, also referredto herein as “peak-to-peak difference” is determined as a measure of themaximum acceleration of the LV wall segment during systole. In oneembodiment, the maximum peak amplitude or peak-to-peak difference of anaccelerometer signal during isovolumic contraction is used as a metricof LV function. Other LV wall motion signal features may additionally oralternatively be determined as indices of LV mechanical function orhemodynamic correlates. Other LV wall motion signal features that may bederived include, but are not limited to, a slope, an integral, afrequency component, or other time or frequency domain characteristics.

If all test A-V intervals have not yet been applied, as determined atdecision step 345, the method 300 returns to step 310 to adjust the A-Vinterval to the next test setting. Once all test A-V intervals have beenapplied, the optimal A-V interval is identified from the stored LV wallmotion data at step 350.

FIG. 6 is a graph of sample, experimental LV wall motion data collectedfrom an accelerometer during atrio-biventricular pacing at varying A-Vintervals and simultaneous right and left ventricular pacing (V-Vinterval set to 0 ms). As A-V interval is increased from 90 ms to 200ms, the maximum LV acceleration and peak-to-peak acceleration decreaseto a plateau point or “saddle point,” then increase again. In oneembodiment, the optimal A-V interval is selected as an A-V intervalcorresponding to the plateau or “saddle” point found by plotting aderived LV wall motion parameter as a function of A-V interval. In theexample shown in FIG. 6, the derived parameter is the peak-to-peakdifference of an accelerometer signal. Based on this parameter, and thecriteria described above, an optimal A-V interval can be identified as130 ms. Shorter A-V intervals can result in overlapping of left atrialand ventricular contraction and abrupt truncation of atrial contraction,resulting in an overall inefficient ejection of blood from theventricles and mitral valve regurgitation. Longer A-V intervals areundesirable because of fusion between the atrial and ventricular fillingphases of the cardiac cycle resulting in altered ventricular fillingpatterns. Reference is made to Leung S K et al., Pacing ClinElectrophysiol. 2000;23:1762-6.

When method 300 is executed by an external pacing system, LV wall motiondata may be displayed in real-time or stored and presented following anoptimization procedure. When method 300 for identifying an optimal A-Vinterval is executed by an implanted device, LV wall motion data may bestored for later uplinking to an external device for display and reviewby a physician. After identifying the optimal A-V interval, the A-Vinterval setting may be automatically adjusted according to method 200described above.

FIG. 7 is a flow chart summarizing steps included in a method fordetermining an optimal V-V interval based on left ventricular wallmotion for use in method 200 of FIG. 4. At step 405, the A-V interval isprogrammed to an optimal setting determined according to method 300 ofFIG. 4. At step 410, the V-V interval is set to a test interval. A rangeof test intervals are predefined and may be delivered in a random,generally increasing, or generally decreasing fashion. A range of testintervals may include intervals that result in the right ventricle beingpaced prior to the left ventricle and intervals that result in the leftventricle being paced prior to the right ventricle. A set of exemplarytest intervals includes right ventricular pacing 20 ms and 40 ms priorto left ventricular pacing, simultaneous left and right ventricularpacing (a V-V interval of 0 ms), and left ventricular pacing 20 ms and40 ms prior to the right ventricle.

Method 400 proceeds to determine the optimal V-V interval in a mannersimilar to method 300 for determining the optimal A-V interval describedabove. A data collection window is set at step 415, and LV wall motiondata is collected for a predetermined time interval or number of cardiaccycles at step 420 during the data collection window applied to eachcardiac cycle. After verifying a stable heart rate at step 425, signalaveraging is performed at step 430 allowing an average peak amplitude oraverage peak-to-peak difference or other signal characteristic to bedetermined at step 435. After all test V-V intervals are applied asdetermined at decision step 440, the optimal V-V interval is identifiedat step 445.

FIG. 8 is a graph of sample, experimental LV wall motion data collectedfrom an accelerometer during atrio-biventricular pacing at varying V-Vintervals and an A-V interval previously optimized to 130 ms.Simultaneous right and left ventricular pacing occurs at a V-V intervalof 0 ms. A convention of negative V-V intervals indicates the leftventricle is paced earlier than the right ventricle, and positive V-Vintervals indicates right ventricular pacing occurs earlier than leftventricular pacing. In one embodiment, the optimal V-V interval isselected as the interval producing the maximum LV wall segmentacceleration based on the maximum peak amplitude, peak-to-peakdifference, or based on a fiducial point of an accelerometer signal. Inthe example shown, the optimal V-V interval may be identified, based onmaximum LV acceleration, as a 40 ms interval with the right ventriclepaced first and the left ventricle paced second.

When method 400 is executed by an external pacing system, LV wall motiondata may be displayed in real-time or stored and presented following anoptimization procedure. When method 400 for identifying an optimal V-Vinterval is executed by an implanted device, LV wall motion data may bestored for later uplinking to an external device for display and reviewby a physician. After identifying the optimal V-V interval, the V-Vinterval setting may be automatically adjusted according to method 200described above.

As noted previously, after adjusting the V-V interval to an optimalsetting, verification that the A-V interval is still optimal may bedesired (step 230, FIG. 4). In order to re-optimize the A-V interval,method 300 may be performed as described above with the V-V intervalprogrammed to the optimal setting identified by method 400 rather than anominal setting. If a different A-V interval is found to be optimal, theA-V interval setting may be adjusted appropriately.

It is contemplated that optimization of A-V and V-V intervals based onLV wall motion according to the methods above may be performed inconjunction with an assessment of other wall segment motion, such as theRV apex. In particular, it may be desired to verify that other wallsegment motion has not been degraded due to optimization of LV wallmotion. It may also be desirable to optimize one or more pacingintervals based on LV wall motion and other pacing intervals based on RVapical wall motion or the motion of other wall segments.

FIG. 9 is a flow chart summarizing steps included in a method formonitoring left ventricular function based on lateral wall motion. Asindicated previously, evaluation of left ventricular function is ofinterest for both diagnostic and therapeutic applications. Thus, it isrecognized, that aspects of the present invention may be employed formonitoring purposes without optimization of a therapy delivery. As such,method 500 summarized in FIG. 9 may be implemented in an implantable orexternal device, such as the devices those shown in FIGS. 1A, 1B andFIG. 3, for monitoring LV function by deriving and storing an LV wallmotion parameter from a sensed LV wall motion signal. The therapydelivery functions of such devices may be selectively disabled or, ifenabled, the optimization of cardiac pacing intervals based on LV wallmotion may be selectively enabled or disabled. Method 500 mayalternatively be implemented in internal or external devices that do notinclude therapy delivery capabilities, but in association with an LVlead equipped with a wall motion sensor, are capable of processing andstoring LV wall motion data.

LV wall motion may be sensed during a selected phase of the cardiaccycle on a continuous, periodic or triggered basis with the wall motionsignal characteristic determined and stored after each predeterminedinterval of time or number of cardiac or respiratory cycles. Forexample, LV function may be evaluated on a periodic basis such ashourly, daily, weekly, or otherwise. Additionally or alternatively, LVfunction may be evaluated on a triggered basis, which may be a manual orautomatic trigger. Automatic triggers may be designed to occur upon thedetection of predetermined conditions during which LV functionevaluation is desired, such as a particular heart rate range, activity,or other conditions.

In one embodiment, LV wall motion is monitored continuously and storageof LV wall motion data is triggered upon the detection of predetermineddata storage conditions, such as, but not limited to, a heart rate,activity, or a condition relating to LV wall motion. For example, LVwall motion may be sensed continuously, and, if an LV wall motionparameter crosses a threshold or satisfies other predetermined datastorage criteria, LV wall motion parameter(s) are stored.

Manual triggers for LV wall motion sensing and/or data storage may bedelivered by a clinician or by a patient, for example when the patientfeels symptomatic. Methods for manually triggering the storage ofphysiological data in an implantable device are generally described inU.S. Pat. No. 5,987,352 issued to Klein, et al., hereby incorporatedherein by reference in its entirety.

Method 500 begins at step 501 when LV wall motion sensing is enabledaccording to the mode of operation of the monitoring device, which asjust described, may be continuous, periodic, automatically- and/ormanually-triggered monitoring. At step 505, an LV wall motion datacollection window is set as described previously. At step 510, LV wallmotion data is acquired for a predetermined interval of time or numberof cardiac or respiratory cycles. At step 515, heart rate stability isverified as described previously. The wall motion signal is averagedover the number of cardiac cycles collected at step 520 to minimizerespiratory or other noise. At step 525, a characteristic of theaveraged signal is determined and stored as an indication of LVfunction. Other physiologic or parametric data may be stored with the LVfunction data such as heart rate, date and time of day, pacing modalityand parameters, and/or any other physiological data that may be sensedby the monitoring device such as patient activity, blood pressure, etc.

When method 500 is implemented in an implantable device, stored data areavailable through uplink telemetry to an external device for laterdisplay and review by a physician. When method 500 is implemented in anexternal device, a display of LV function data may be updated each timean LV wall motion signal characteristic is determined.

Thus a method and apparatus have been described for monitoring leftventricular cardiac contractility and optimizing a cardiac therapy basedon left ventricular lateral wall acceleration measured using a leftventricular lead equipped with an acceleration sensor. The methodsdescribed herein may advantageously be applied in numerous cardiacmonitoring or therapy modalities including chronic or acute applicationsassociated with implantable or external devices.

As is known in the art, besides the transducers described hereinabove,other types of transducers may be used provided, in general, that suchtransducers are hermetically sealed, are fabricated (on least on theexterior surfaces) of substantially biocompatible materials andappropriately dimensioned for a given application. With respect toappropriate dimension, a transducer intended to transvenous deploymentshould be susceptible of catheter or over-the-wire delivery. Thus, theradial dimension should be on the order of less than about 11 French andpreferably about less than eight French. Also, the transducer should besomewhat supple, and not too long, in the longitudinal dimension so thatthe transducer can safely navigate the venous system, pass through thecoronary sinus and enter vessels branching from the coronary sinus(e.g., the great cardiac vein, and the like). These dimensions can berelaxed for a transducer intended for deployment though a portion of thechest (e.g., a thoracotomy) with an affixation mechanism adapted tomechanically couple adjacent the lateral wall. Two adjacent locationsinclude the epicardium and the pericardium. The dimensions may berelaxed to a greater extent if the epicardial receives the transducer,and to a lesser extent, to a portion of the pericardium. As is wellknown, the pericardium is the membranous sac filled with serous fluidthat encloses the heart and the roots of the aorta and other large bloodvessels. One example of appropriate fixation apparatus for epicedialapplication is a helical tipped lead that is screwed into the surface ofthe epicardium. For pericardial fixation a sealing member (e.g.,compressible gasket or opposing members on each side of the pericardialsac) may be used in addition to an active fixation member such as ahelical tipped lead.

As is also known in the art related to sensors and transducers,accelerometers can be described as two transducers, a primary transducer(typically a single-degree-of-freedom vibrating mass which converts theacceleration into a displacement), and a secondary transducer thatconverts the displacement (of a seismic mass) into an electric signal.Most accelerometers use a piezoelectric element as a secondarytransducer. Piezoelectric devices, when subjected to a strain, output avoltage proportional to the strain, although piezoelectric elementscannot provide a signal under static (e.g., constant acceleration)conditions. Important characteristics of accelerometers include range ofacceleration, frequency response, transverse sensitivity (i.e.sensitivity to motion in the non-active direction), mounting errors,temperature and acoustic noise sensitivity, and mass.

One type of primary transducer, which describe the internal mechanism ofthe accelerometer, include spring-retained seismic mass. In mostaccelerometers, acceleration forces a damped seismic mass that isrestrained by a spring, so that it moves relative to the casing along asingle axis. The secondary transducer then responds to the displacementand/or force associated with the seismic mass. The displacement of themass and the extension of the spring are proportional to theacceleration only when the oscillation is below the natural frequency.Another accelerometer type uses a double-cantilever beam as a primarytransducer which can be modeled as a spring-mass-dashpot, only theseismic mass primary transducer will be discussed.

Types of secondary transducers, which describe how the electric signalis generated from mechanical displacement, include: piezoelectric,potentiometric, reluctive, servo, strain gauge, capacitive, vibratingelement, etc. These are briefly described as an introduction for theuninitiated.

Piezoelectric transducers are often used in vibration-sensingaccelerometers, and sometimes in shock-sensing devices. Thepiezoelectric crystals (e.g., often quartz or ceramic) produce anelectric charge when a force is exerted by the seismic mass under someacceleration. The quartz plates (two or more) are preloaded so that apositive or negative change in the applied force on the crystals resultsin a change in the electric charge. Although the sensitivity ofpiezoelectric accelerometers is relatively low compared with other typesof accelerometers, they have the highest range (up to 100,000 g's) andfrequency response (over 20 kHz).

Potentiometric accelerometers utilize the displacement of thespring-mass system linked mechanically to a wiper arm, which moves alonga potentiometer. The system can use gas, viscous, magnetic-fluid, ormagnetic damping to minimize acoustic noise caused by contact resistanceof the wiper arm. Potentiometric accelerometers typically have afrequency range from zero to 20-60 Hz, depending on the stiffness of thespring, and have a high-level output signal. They also have a lowerfrequency response than most other accelerometers, usually between 15-30Hz.

Reluctive accelerometers use an inductance bridge, similar to that of alinear variable differential transducer to produce an output voltageproportional to the movement of the seismic mass. The displacement ofthe seismic mass in inductance-bridge accelerometers causes theinductances of two coils to vary in opposing directions. The coils actas two arms of an inductance bridge, with resistors as the other twoarms. The AC output voltage of the bridge varies with appliedacceleration. A demodulator can be used to convert the AC signal to DC.An oscillator can be used to generate the required AC current when a DCpower supply is used, as long as the frequency of the AC signal is fargreater than that of the frequency of the acceleration.

In servo accelerometers, acceleration causes a seismic mass “pendulum”to move. When motion is detected by a position-sensing device, a signalis produced that acts as the error signal in the closed-loop servosystem. After the signal has been demodulated and amplified to removethe steady-state component, the signal is passed through a passivedamping network and is applied to a torquing coil located at the axis ofrotation of the mass. The torque developed by the torquing coil isproportional to the current applied, and counteracts the torque actingon the seismic mass due to the acceleration, preventing further motionof the mass. Therefore, the current through the torquing coil isproportional to acceleration. This device can also be used to measureangular acceleration as long as the seismic mass is balanced. Servoaccelerometers provide high accuracy and a high-level output at arelatively high cost, and can be used for very low measuring ranges(well below 1 g).

Strain gauge accelerometers, often called “piezoresistive”accelerometers, use strain gauges acting as arms of a Wheatstone bridgeto convert mechanical strain to a DC output voltage. The gauges areeither mounted to the spring, or between the seismic mass and thestationary frame. The strain gauge windings contribute to the springaction and are stressed (i.e., two in tension, two in compression), anda DC output voltage is generated by the four arms of the bridge that isproportional to the applied acceleration.

These accelerometers can be made more sensitive with the use ofsemiconductor gauges and stiffer springs, yielding higher frequencyresponse and output signal amplitude. Unlike other types ofaccelerometers, strain gauge accelerometers respond to steady-stateaccelerations.

In a capactivie accelerometer a change in acceleration causes a changein the space between the moving and fixed electrodes of a capacitiveaccelerometer. The moving electrode is typically a diaphragm-supportedseismic mass or a flexure-supported, disk-shaped seismic mass. Theelement can act as the capacitor in the LC or RC portion of anoscillator circuit. The resulting output frequency is proportional tothe applied acceleration.

In a vibrating element accelerometer, a very small displacement of theseismic mass varies the tension of a tungsten wire in a permanentmagnetic field. A current through the wire in the presence of themagnetic field causes the wire to vibrate at its resonant frequency(like a guitar string). The circuitry then outputs a frequencymodulation (deviation from a center frequency) that is proportional tothe applied acceleration. Although the precision of such a device ishigh, it is quite sensitive to temperature variations and is relativelyexpensive.

Thus, those of skill in the art will recognize that while the presentinvention has been described herein in the context of specificembodiments, it is recognized that numerous variations of theseembodiments may be employed without departing from the scope of thepresent invention. The descriptions provided herein are thus intended tobe exemplary, not limiting, with regard to the following claims.

1. A method for monitoring left ventricular function during delivery ofa cardiac resynchronization therapy (CRT), comprising: deploying amotion sensor to a fixed location on a portion of a left ventricularlateral wall wherein the motion sensor generates a motion signalproportional to motion of the portion of the left ventricular lateralwall; opening a data collection window during a portion of a selectedcardiac cycle phase; storing the motion signal throughout at least apart of the portion of the data collection window for a predeterminedtime interval or for more than one cardiac cycle; verifying a heart ratestability characteristic during the predetermined time interval or formore than one cardiac cycle averaging the stored motion signal;determining a signal characteristic from the averaged stored signal thatis representative of left ventricular function; and delivering a cardiacresynchronization therapy (CRT) based at least in part upon the signalcharacteristic; wherein the motion sensor consists of one from thegroup: a piezoelectric sensor, an optical sensor, a Hall-effect typesensor, a capacitive sensor, a resistive sensor, an inductive sensor. 2.A method according to claim 1, wherein said motion sensor is adapted tobe disposed in a portion of the coronary sinus vessel or a blood vesselfluidly coupled to said coronary sinus.
 3. A method according to claim1, wherein said motion sensor is adapted to be disposed adjacent to aportion of the epicardium of the left ventricle of the heart.
 4. Amethod according to claim 3, wherein the portion of the lateral wall isa basal portion of the lateral wall.
 5. A method according to claim 4,wherein the portion of the lateral wall is a mid-basal portion of thelateral wall.
 6. A method according to claim 1, wherein said motionsensor is adapted to be disposed within the pericardium of the heart. 7.A method according to claim 1, wherein said motion sensor is operativelycoupled to an implantable medical device (IMD) and said IMD operativelycouples to a first pacing electrode and a second pacing electrode.
 8. Amethod according to claim 7, wherein the first pacing electrode or thesecond pacing electrode further comprises a sense electrode inelectrical communication with a sensing circuit coupled to the IMD.
 9. Amethod according to claim 7, wherein the first pacing electrode or thesecond pacing electrode comprises a sense electrode in electricalcommunication with a sensing circuit coupled to the IMD.
 10. A methodfor optimizing cardiac pacing intervals based on left ventricularfunction for delivery of a cardiac resynchronization therapy (CRT),comprising; placing a motion sensor into operative mechanicalcommunication with a portion of a left ventricular lateral free wall sothat the motion sensor generates a motion signal proportional to themotion of the left ventricular lateral free wall; enabling a temporaldata collection window corresponding to a selected cardiac cycle phase;applying a cardiac pacing stimulus delivered according to a preselectedset of test pacing parameters; sensing the motion signal during at leasta part of the temporal data collection window or during a more than onecardiac cycle for at least some members of the preselected set of testpacing parameters; verifying a heart rate stability characteristic;averaging the motion signal for the at least some members of thepreselected set of test pacing parameters; determining a signalcharacteristic from the averaged sensed signal that is representative ofrelatively improved left ventricular function during each of theselected test pacing parameters; storing a cardiac pacing timingparameter for a right ventricular pacing electrode and for a leftventricular pacing electrode that resulted in the relatively improvedleft ventricular function; delivering a cardiac resynchronizationtherapy (CRT) based upon the cardiac pacing timing parameter, whereinthe motion sensor consists of one from the group; a piezoelectricsensor, an optical sensor, a Hall-effect type sensor, a capacitivesensor, a resistive sensor, an inductive sensor.
 11. A method formonitoring left ventricular function during delivery of a cardiacresynchronization therapy (CRT), comprising: deploying a motion sensorto a portion of a left ventricular lateral wall of a patient's heart,wherein the motion sensor generates motion signals proportional tomotion of the portion of the left ventricular lateral wall andindicative of left ventricular function; storing the motion signalsthroughout at least portions of a plurality of cardiac cycles; verifyinga heart rate stability characteristic during the plurality of cardiaccycles; determining a signal characteristic from the stored motionsignals that is representative of left ventricular function; anddependant upon the verified heart rate stability characteristic,delivering a cardiac resynchronization therapy (CRT) based upon thesignal characteristic to optimize left ventricular function.
 12. Amethod according to claim 11, wherein said motion sensor is deployed ina portion of a coronary sinus vessel or a blood vessel fluidly coupledto said coronary sinus.
 13. A method according to claim 11, wherein saidmotion sensor is deployed adjacent to a portion of the epicardium of theleft ventricle of the heart.
 14. A method according to claim 11, whereinsaid motion sensor is deployed within the pericardium of the patient'sheart.
 15. A method according to claim 11, wherein said motion sensor isoperatively coupled to an implantable medical device (IMD) and said IMDoperatively couples to a first pacing electrode and a second pacingelectrode.
 16. A method for optimizing cardiac pacing intervals based onleft ventricular function for delivery of a cardiac resynchronizationtherapy (CRT) of a patient's heart, comprising; placing a motion sensorinto operative mechanical communication with a portion of a leftventricular lateral free wall of the patient's heart so that the motionsensor generates motion signals proportional to the motion of the leftventricular lateral free wall and indicative of left ventricularfunction; applying cardiac pacing stimuli delivered according to apreselected set of test pacing parameters; sensing the motion signalduring at least a part of a plurality of cardiac cycles for at leastsome members of the preselected set of test pacing parameters; verifyinga heart rate stability characteristic; determining a signalcharacteristic from the sensed signals that is representative ofrelatively improved left ventricular function during each of theselected test pacing parameters; storing a cardiac pacing parameter thatresulted in the relatively improved left ventricular function; anddependant upon the verified heart rate stability characteristic,delivering a cardiac resynchronization therapy (CRT) based upon thestored cardiac pacing parameter.
 17. A method according to claim 16,wherein said motion sensor is deployed in a portion of a coronary sinusvessel or a blood vessel fluidly coupled to said coronary sinus.
 18. Amethod according to claim 16, wherein said motion sensor is deployedadjacent to a portion of the epicardium of the left ventricle of theheart.
 19. A method according to claim 16, wherein said motion sensor isdeployed within the pericardium of the patient's heart.
 20. A methodaccording to claim 16, wherein said motion sensor is operatively coupledto an implantable medical device (IMD) and said IMD operatively couplesto a first pacing electrode and a second pacing electrode.
 21. A methodaccording to claim 20, wherein the first pacing electrode or the secondpacing electrode comprises a sense electrode in electrical communicationwith a sensing circuit coupled to the IMD.